The present invention relates to a method and devices for changing longitudinal video recordings with or without audio information in recording/playback systems employing recording media having parallel tracks, especially magnetic tracks, which contain originally recorded signals which can be read by means of a playback head and recorded by means of a recording head.
In the case of video tapes in which information is recorded on longitudinal tracks, it is possible to record sound on separate tracks or on the guard bands between the video tracks. However, if, for the purpose of making better use of the magnetic tape capacity or of avoiding disturbances, video and audio signals are combined and recorded on one magnetic track, subsequent modification of the audio information, without affecting the video information, can according to the prior art only be performed on a second video recorder.
German Published Application DAS 1,063,397 discloses, in connection with sound recordings, that an originally recorded audio signal, after scanning, can be mixed with a sound recording and recorded on a new track adjacent to the non-erased track carrying the original audio signal. For this purpose, twice the number of tracks and hence a large supply of tape is required. It is also known from German Published Application DAS 1,071,367 that, in the making of a sound recording, an additional recording can be accommodated on part of the track width of the first recording. In practice, this is effected by partly overwriting the first recording, using a smaller track width, or by using two fixed recording heads displaced relative to the track carrying the first recording, or by employing a single vertically displaceable recording head. Such an overwriting operation necessitates the separate recording of the video and audio signals on different tracks.
Furthermore, German Laid-Open Application DOS 2,457,636 discloses that audio information can be written over video information by means of a separate head having an inclined gap. Here, the difficulty is to separate the video and audio signals satisfactorily from one another during playback.